1. Field of the Invention
This invention relates generally to disk apparatuses and, more particularly, to a disk apparatus which illuminates laser light to a disk, such as an MO (Magneto-Optical) disk to record and/or reproduce signals.
2. Description of the Prior Art
In the conventional disk apparatus of this kind, when turning on the power to the apparatus main body or exchanging a disk, the objective lens provided on an optical pickup is moved from its lowermost position to an uppermost position to thereby detect a focal point of the objective lens. Incidentally, the objective lens may be moved from the upper-most to the lowermost position. After positioning the objective lens in a focal point, focus servo and tracking servo processing is carried out to allow the objective lens to follow the track.
However, in the prior art, the objective lens is gradually moved from its lowermost position to the uppermost position in order to perform focus servo in a position where the focus error signal becomes nearly zero. Due to this, it takes a long time before carrying out focus servo. In addition, there exists surface deflection in the disk. Consequently, in the event that the objective lens moving from the lowermost to uppermost position is unsuccessfully introduces a track, there is a need of performing again the operation for detecting a focal point from the beginning.
Therefore, it is a primary object of the present invention to provide a disk apparatus that positioning is made to a focal point in a brief time.
The present invention is a disk apparatus, comprising: a laser for emitting laser light; an objective lens for converging and illuminating laser light to a disk surface; producing means for producing a focus-related signal based on laser light reflected upon the disk surface; first moving means for moving the objective lens within a first range with respect to a focussing direction; determining means for determining a second predetermined range including a focal position and narrower than the first predetermined range, based on the focus-related signal produced upon moving the objective lens within the first predetermined range; second moving means for repeatedly moving the objective lens within the second predetermined range; and detecting means for detecting the focal position based on the focus-related signal produced upon moving the objective lens within the second predetermined range.
In this disk apparatus, the laser light emitted from the laser is converged by the objective lens and illuminated to a disk recording/reproducing surface. A focus-related signal is produced based on the light reflected upon the disk recording/reproducing surface. The determining means determines a second predetermined range narrower than a first predetermined range including a focal point, based on the focus-related signal produced upon moving the objective lens in the first predetermined range. Then, the detecting means detects a focal point based on the focus-related signal when moving the objective lens in the second predetermined range. That is, high-speed focus servo is possible to apply because the objective lens is moved in the second predetermined range narrower than the first predetermined range. Also, because of movement repetition, it is possible to detect a focal point without requiring redoing focal positioning operation from the beginning even where focal point is difficult to detect due to surface deflection of the disk.
According to this invention, because a focal point is detected by moving the objective lens in the second predetermined range narrower than the first predetermined range, focal positioning is possible in a brief time.
Also, the repetition of movement in the second predetermined range makes it possible to detect a focal point without redoing focal positioning operation from the beginning even where a focal point is difficult to detect due to surface deflection of the disk.
In one aspect of the invention, error signal producing means performs predetermined operation processing on outputs of the plurality of photodetector elements to produce a focus error signal, and the detecting means detects a focal point based on the focus error signal.
In one embodiment of the invention, first lens position detecting means detects a first lens position where the focus error signal is minimized in level, and second lens position detecting means detects a second lens position where the focus error signal is maximized in level. Calculating means calculates a middle point of the first lens position and the second lens position, and second predetermined range determining means determines as the second predetermined range a range having the middle position as a center and narrower than the first predetermined range.
In another embodiment of the invention, adding signal producing means produces an addition (SUM) signal. A second predetermined range is determined using the SUM signal.
In still another embodiment of the invention, when the objective lens moves in the first predetermined range, particular lens position detecting means detects two lens positions where the SUM signal level is a predetermined level. The calculating means calculates an approximate middle point using the two lens positions, and the determining means determines the second predetermined position including the middle point.
In yet another embodiment of the invention, the second predetermined range is related to an amount of surface deflection of the disk. That is, the second predetermined range is a range to be determined by adding or subtracting an absolute value of a surface deflection amount by the use of the middle point as a center.
In another embodiment of the invention, once the second predetermined range is determined, absolute value detecting means detects an absolute value of the focus error signal when the objective lens moves in one direction. Enabling means enables focus servo when the absolute value after exceeding the first predetermined value goes below the second predetermined value. Thus, the objective lens can be positioned to a focal point.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.